TL;DR
Uneven temperature is almost always a duct leak, a closed damper, or a disconnected branch duct. Walk the duct system and check each branch damper position before balancing.
What you might see
- some zones significantly warmer than others
- hot spots near exterior walls or windows
- temperature difference greater than 4 degF across the space
- supply air velocity low at distant diffusers
Likely causes
Zone damper stuck closed or failed actuator preventing conditioned air from reaching a zone
Duct leak or disconnected branch duct dumping conditioned air into the plenum or ceiling cavity
Supply duct undersized for the total airflow, causing excessive velocity loss at far branches
Excessive return air restriction reducing total system airflow and cooling capacity
Required tools
- Anemometer or manometer (airflow measurement)
- Digital thermometer
- Foil tape and mastic sealant (duct repair)
- LOTO kit
Safety first
- Lock out the unit before accessing ductwork in the air handler section.
- Attic or ceiling plenum spaces may have limited access and extreme heat. Allow the space to cool before entering.
Procedure
- 1
Map the temperature at multiple points across the space with a thermometer. Identify which zones are warmest.
- 2
Lock out the unit before accessing ductwork.
- 3
Locate all zone dampers serving the warm zones. Manually verify each damper is in the open position and the actuator arm is connected.[1]
- 4
Inspect accessible duct sections for disconnected flex duct, pulled connections, or large gaps at branch fittings. Reconnect and seal with mastic or foil tape.[1]
- 5
Measure supply air velocity at the diffusers in the warm zones with an anemometer. Low velocity at a distant diffuser combined with high velocity at a near diffuser indicates a branch balance problem.
- 6
Adjust volume dampers to re-balance the system. Partially close near branches to divert more flow to distant zones. Adjust in 15-degree increments and allow 15 minutes for the space to respond.
- 7
After balancing, verify return air grilles are not blocked by furniture or equipment, which restricts total system airflow.
Sources
Trane Voyager Commercial Rooftop Service Literature, Trane (Trane Technologies)
Trane Voyager Commercial Rooftop IOM, duct system balancing and damper adjustment procedures (general)
View source
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